Paul,
I have use a single throw toggle switch from Home Depot. I have used these for over 10 years, it is a positive shut off and works great with helpers that are not familiar with E power. Yes, you do have to be carefull once you plug in but this goes for external plugs also. For contests I usually plug the pack in once I get to the circle then arm the system once I give the hand signal to begin the flight. At the end of the flight I have the helper shut off the switch and hold the airplane until I can get to it to unplug the pack.
Best, DennisT